Torque transfer pulleys are used in many applications, such as to couple a remote device (such as an alternator or a supercharger) to a rotating system (such as an engine). The pulley may include a drive surface to be driven by the rotating system and may be coupled to a shaft that is coupled to the remote device. Several types of conventional torque transfer pulleys are depicted in FIG. 11. In each graph, the left side of the graph (negative angular displacement) corresponds to the relative rotation of a pulley with respect to a shaft coupled to the pulley in a direction counter to the direction of pulley rotation (for example, when the pulley is spinning slower than the drive shaft, or an overrun condition in embodiments where the pulley includes an overrunning clutch mechanism). This type of rotation is also referred to as rotation in a counter torque direction. The right side of each graph (positive angular displacement) corresponds to a relative rotation of the pulley in the same direction as the direction of pulley rotation (for example, when the pulley is spinning faster than the shaft). This type of rotation is also referred to as rotation in the torque direction.
In the upper left quadrant, a graph of the response of a solid pulley is shown. As seen by the line 1102, as the pulley is solid, there is zero angular displacement and 100 percent of the torque is transferred by the pulley to the shaft immediately, without any relative displacement between the pulley and the shaft. As the pulley does not overrun, it holds/brakes the drive belt 100 percent as per the solid vertical line below the origin. Such designs undesirably offer no decoupling of the rotor's rotational inertia from the pulsations of an internal combustion engine in the torque direction, and no overrun in the counter torque direction during sudden engine speed changes.
In the upper right quadrant, a graph of the response of a pulley having a free spin overrunning clutch is shown. As seen by the line 1104, the pulley transfers essentially 100 percent of the torque immediately, as per the solid vertical line above origin, upon rotation in the torque direction. The pulley also overruns immediately in the counter torque direction, so the belt is separated from the rotor inertia, as shown by the flat line at zero torque extending in the counter torque direction. Such pulley designs offer no springy engagement in the torque direction, and therefore are not frequency tunable to decouple the rotor's inertia from the engine's pulsations.
In the lower left quadrant, a graph of the response of a pulley having a free spin isolating decoupler is shown. As seen by the line 1106, the pulley transfers gradually increasing torque as per the upward sloping straight line extending in the torque direction. The pulley overruns immediately in the counter-torque direction, so the belt is separated from the rotor inertia. This pulley design offers springy engagement in the torque direction, therefore, is frequency tunable to decouple the rotor's inertia from the engine's pulsations. However, this pulley design typically employs a metallic torsional spring system that is not durable and is highly dependent on lubrication. Thus, lubrication retention is also necessary, which leads to additional complexities in the design and higher costs. Force vectors and the friction clutch overrun functions limit the choices of alternate materials for the body, such as thermoplastics and thermosets.
In the lower right quadrant, a graph of the response of an elastomeric spring pulley having a controlled overrun decoupler is shown. As seen by the line 1108, the pulley overruns up to a very limited range of angular travel, then quickly becomes asymptotic as springs within the pulley become completely engaged. Thus, this pulley design offers very limited overrun in the counter torque direction, then quickly behaves as a solid pulley. This pulley offers springy connection in the torque direction, but inventors have observed that the angular range is too limited, pushing the springs to operate near or at the asymptotic portion of the curve, causing the effective stiffness of the pulley to be too high in certain applications. The inventors have further observed that the high effective stiffness increases the pulley's natural frequency which can lead to resonance issues. The inventors believe that the limited angular range of motion of this pulley design forces the use of a spring system that is, from the onset, too stiff for some engine applications. Moreover, the inventors further believe that the overrun is too limited to properly manage sudden engine speed changes in certain engines sizes and types, particularly as alternators increase in output (i.e., present greater rotational inertia) given ever increasing vehicle electrical demands. The inventors believe that this highly constrained overrun may cause the belt to jump off the front end accessory drive (FEAD) path, as well as contribute to noise, vibration, and harshness (NVH). The lack of significant overrun also undermines benefits in fuel economy.
The inventors have observed that the limited range of the prior art can cause the spring material to fail under higher engine torque loads, such as under engine lugging conditions in manual transmission vehicles or in high amperage alternators or in diesel engines. In such circumstances, for example, the spring materials are so compressed that they can be pushed into minimal yet necessary radial voids between the interacting paddles, essentially pinching and shredding the springs. In another scenario of prior art, the limited range can push to springs into such deformation, beyond the material's limits, as to trigger hysteresis and/or catastrophic spring failure.
Thus, the inventors have provided improved overrunning pulley designs that address one or more of the above deficiencies in the prior art.